Using obstacle clearance to measure precise lateral gap

ABSTRACT

A system and method is provided for identifying an object along a road, where the object may be represented by a bounding box, and projecting a set of obstacle points within the bounding box corresponding to the identified object. In one aspect, a two-dimensional plane oriented perpendicular to a direction of the movement of the vehicle may be identified. In another aspect, the areas of the plane that may be occupied based on the set of obstacle points may be determined to generate a contour of the identified object. Thereafter, the height profiles of the identified object and the vehicle may be determined and identified, respectively. Based on the height profiles, a minimum clearance may be determined.

The present application is a continuation of U.S. patent applicationSer. No. 14/452,860, filed Aug. 6, 2014, the disclosure of which isincorporated herein by reference.

BACKGROUND

Autonomous vehicles, such as vehicles which do not require a humandriver, may be used to aid in the transport of passengers or items fromone location to another. An important component of an autonomous vehicleis the perception system, which allows the vehicle to perceive andinterpret its surroundings using cameras, radar, sensors, and othersimilar devices. The perception system executes numerous decisions whilethe autonomous vehicle is in motion, such as speeding up, slowing down,stopping, turning, etc. Autonomous vehicles may also use the cameras,sensors, and global positioning devices to gather and interpret imagesand sensor data about its surrounding environment, e.g., parked cars,trees, buildings, etc. These images and sensor data allow the vehicle tosafely maneuver itself around various objects.

For example, the perception system may interpret an object as a boundingbox. A bounding box may be a virtual, three-dimensional box thatentirely encloses the object. In this regard, the perception system mayspatially identify where the object is relative to the vehicle and avoidhitting the bounding box. However, maneuvering around or under complexobjects, such as a tree branch overhanging a road, may be difficultusing a bounding box.

BRIEF SUMMARY

In one aspect, a method comprises identifying, using one or morecomputing devices, an object along a road, wherein the object isrepresented by a bounding box, and projecting, using the one or morecomputing devices, a set of obstacle points within the bounding boxcorresponding to the identified object. Moreover, the method comprisesidentifying, using the one or more computing devices, a two-dimensionalplane oriented perpendicular to a direction of movement of the vehicle,and determining, using the one or more computing devices, which areas ofthe two-dimensional plane are occupied based on the set of obstaclepoints to generate a contour of the identified object. The methodfurther comprises determining, using the one or more computing devices,a height profile of the identified object, identifying, using the one ormore computing devices, a height profile of the vehicle, anddetermining, using the one or more computing devices, a minimumclearance based on the height profile of the identified object and theheight profile of the vehicle.

In another aspect, a system is provided comprising a memory and one ormore computing devices, each of the one or more computing devices havingone or more processors, the one or more computing devices being coupledto the memory. The one or more computing devices are configured toidentify an object along a road, wherein the object is represented by abounding box, and project a set of obstacle points within the boundingbox corresponding to the identified object. Moreover, the one or morecomputing devices are configured to identify a two-dimensional planeoriented perpendicular to a direction of movement of the vehicle, anddetermine which areas of the two-dimensional plane are occupied based onthe set of obstacle points to generate a contour of the identifiedobject. The one or more computing devices are further configured todetermine a height profile of the identified object, identify a heightprofile of the vehicle, and determine a minimum clearance based on theheight profile of the identified object and the height profile of thevehicle.

In yet another aspect, a non-transitory, tangible computer-readablemedium on which instructions are stored, the instructions, when executedby one or more computing devices perform a method, the method comprisesidentifying an object along a road, wherein the object is represented bya bounding box, and projecting a set of obstacle points within thebounding box corresponding to the identified object. Moreover, themethod comprises identifying a two-dimensional plane orientedperpendicular to a direction of movement of the vehicle, and determiningwhich areas of the two-dimensional plane are occupied based on the setof obstacle points to generate a contour of the identified object. Themethod further comprises determining a height profile of the identifiedobject, identifying a height profile of the vehicle, and determining aminimum clearance based on the height profile of the identified objectand the height profile of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a functional diagram of a system in accordance with aspectsof the disclosure.

FIG. 1B is an example illustration of the vehicle of FIG. 1A inaccordance with aspects of the disclosure.

FIG. 2 is an example data describing a height profile of a vehicle inaccordance with aspects of the disclosure.

FIG. 3 is an example illustration of object detection in accordance withaspects of the disclosure.

FIG. 4A is an example bounding box of an object in accordance withaspects of the disclosure.

FIG. 4B is an example set of obstacle points in accordance with aspectsof the disclosure.

FIG. 4C is an example two-dimensional contour in accordance with aspectsof the disclosure.

FIG. 5 is an example computation of minimum clearance measurement inaccordance with aspects of the disclosure.

FIG. 6 is an example flow diagram in accordance with aspects of thedisclosure.

DETAILED DESCRIPTION

The present disclosure relates to allowing a vehicle to maneuver aroundor underneath other objects in an autonomous driving mode. For example,a perception system of an autonomous vehicle may compute a minimumhorizontal clearance measurement to determine whether the vehicle canmaneuver around or under a complex object. In one scenario, the complexobject may be a tree with a large overhanging branch. As such, theperception system may calculate lateral distances between the center ofthe autonomous vehicle and the tree at a plurality of heightmeasurements to generate a two-dimensional height profile of the tree.Then, the difference between the tree's height profile and the vehicle'sheight profile may be computed to determine a minimum clearancemeasurement. This information may be used to determine whether thevehicle can safely maneuver under and/or around the tree.

In order to determine how the vehicle will fit next to or under variousobjects, a virtual model of the vehicle and its respective heightprofile may be generated. For example, a height profile of the vehiclemay be based on the virtual model. The height profile may be generatedby computing a lateral distance from the center to one or both sides ofthe vehicle (e.g., right side-view mirror, left side-view mirror) atvarious height measurements ascending from bottom to top of the vehicle,or vice versa. For instance, the vehicle's height profile may include anarray of (x, y) values, where “x” is the vehicle width and “y” is theheight.

The perception system of an autonomous vehicle may compute minimumclearance measurements between objects and the vehicle at intervaledsteps along a road. For example, the intervaled steps may be every 0.25meters or more or less. At each step, the perception system may identifya set of nearby objects and discard the objects that are far away fromtrajectory based on a threshold distance. For example, the perceptionsystem may perform analysis on objects that are within 15 meters of thevehicle's trajectory and temporarily disregard objects that are outsidethe threshold distance of 15 meters.

Thus, the perception system may first detect objects in the vehicle'senvironment. For example, the perception system may detect a treeoverhanging a road as a series of coordinate points and arrange thosepoints into a three-dimensional bounding box. The tree's bounding boxmay also contain a plurality of obstacles, such as overhanging branches,leaves, etc. In that regard, if the top of the tree protrudes out intothe road, so may the bounding box.

If the tree is within the threshold distance, the perception system mayproject the coordinate points of the bounding box into a two-dimensionalgrid oriented perpendicular to the vehicle's direction of movement. Foreach intervaled step along the road, the two-dimensional grid may be adifferent cross-section or “slice” of the bounding box of a tree. Inthis regard, the perception system may perform analysis on one slice ofthe bounding box of a tree at a time. The grid may also contain aplurality of cells. Subsequently, the perception system may determine atwo-dimensional contour of the complex object for the selected slicebased on which cells of the grid are occupied by the projected points.

This contour may be used to determine a height profile for the tree. Forexample, a lateral distance may be measured from the center of thevehicle to an edge of the contour at a height measurement of 0.2 metersfrom the ground. Then, another lateral distance may be measured at aheight measurement of 0.4 meters, and so on, until a set of lateraldistances are measured. At minimum, the set may include the lateraldistances that cover the height of the vehicle.

In that regard, the perception system may compare the contour of anobject and the virtual model of the vehicle to compute a minimumclearance measurement for the object and the vehicle. By computing thedifference between the object's height profile and the car's heightprofile, a minimum clearance measurement may be determined. This minimumclearance measurement may then be used to determine how the vehicle willdrive around or under the object.

In addition, a threshold minimum horizontal distance may be used toprevent the vehicle from getting too close to the object. As an example,the threshold may be set at 0.13 meters. Thus, when the computed minimumclearance measurement is less than 0.13 meters, the perception systemmay determine that the vehicle will be too close to the object.

The above-described aspects allow autonomous vehicles and associatedsystems to compute more refined lateral clearance values ofthree-dimensional complex objects having asymmetrical structures. Inthat regard, an autonomous vehicle may determine when it would be safeto drive around or under a complex object, such as a tree, such that nopoint on the vehicle is horizontally too close to the tree.

As shown in FIG. 1A, a vehicle 100 in accordance with one aspect of thedisclosure includes various components. While certain aspects of thedisclosure are particularly useful in connection with specific types ofvehicles, the vehicle may be any type of vehicle including, but notlimited to, cars, trucks, motorcycles, busses, boats, airplanes,helicopters, lawnmowers, recreational vehicles, amusement park vehicles,farm equipment, construction equipment, trams, golf carts, trains, andtrolleys. The vehicle may have one or more computing devices, such ascomputing device 110 containing one or more processors 120, memory 130and other components typically present in general purpose computingdevices.

The memory 130 stores information accessible by the one or moreprocessors 120, including data 132 and instructions 134 that may beexecuted or otherwise used by the processor(s) 120. The memory 130 maybe of any type capable of storing information accessible by theprocessor(s), including a computing device-readable medium, or othermedium that stores data that may be read with the aid of an electronicdevice, such as a hard-drive, memory card, ROM, RAM, DVD or otheroptical disks, as well as other write-capable and read-only memories.Systems and methods may include different combinations of the foregoing,whereby different portions of the instructions and data are stored ondifferent types of media.

The data 132 may be retrieved, stored or modified by processor(s) 120 inaccordance with the instructions 132. For instance, although the claimedsubject matter is not limited by any particular data structure, the datamay be stored in computing device registers, in a relational database asa table having a plurality of different fields and records, XMLdocuments or flat files. The data may also be formatted in any computingdevice-readable format.

For example, data 132 may include a height profile of the vehicle 100.The height profile may be based on a virtual model of the vehicle 100.The virtual model represents a general three-dimensional shape,dimension, and/or geometry of the vehicle 100. As will be furtherdiscussed below, the one or more processors 120 of computing device 110may compute a set of lateral clearance measurements from the vehicle toa particular object based at least in part on the height profile of thevehicle.

In another example, data 132 may also include at least one or morepredetermined threshold clearance values to ensure that a vehicle doesnot get too close to an object. In other words, the predeterminedthreshold clearance may be a safety buffer between the vehicle and theobject. In that regard, the threshold clearance may be an extra safetyfeature for an autonomous vehicle.

The instructions 134 may be any set of instructions to be executeddirectly (such as machine code) or indirectly (such as scripts) by theprocessor. For example, the instructions may be stored as computingdevice code on the computing device-readable medium. In that regard, theterms “instructions” and “programs” may be used interchangeably herein.The instructions may be stored in object code format for directprocessing by the processor, or in any other computing device languageincluding scripts or collections of independent source code modules thatare interpreted on demand or compiled in advance. Functions, methods androutines of the instructions are explained in more detail below.

The one or more processors 120 may be any conventional processors, suchas commercially available CPUs. Alternatively, the one or moreprocessors may be a dedicated device such as an ASIC or otherhardware-based processor, such as a field programmable gate array(FPGA). Although FIG. 1A functionally illustrates the processor(s),memory, and other elements of computing device 110 as being within thesame block, it will be understood by those of ordinary skill in the artthat the processor, computing device, or memory may actually includemultiple processors, computing devices, or memories that may or may notbe stored within the same physical housing. For example, memory may be ahard drive or other storage media located in a housing different fromthat of computing device 110. Accordingly, references to a processor orcomputing device will be understood to include references to acollection of processors or computing devices or memories that may ormay not operate in parallel.

Computing device 110 may have all of the components normally used inconnection with a computing device such as the processor and memorydescribed above, as well as a user input 150 (e.g., a mouse, keyboard,touch screen and/or microphone) and various electronic displays (e.g., amonitor having a screen, a small LCD touch-screen or any otherelectrical device that is operable to display information). In thisexample, the vehicle includes an internal electronic display 152 as wellas an external electronic display 154. In this regard, internalelectronic display 152 may be located within a cabin of vehicle 100 andmay be used by computing device 110 to provide information to passengerswithin the vehicle 100. External electronic display 154 may be locatedeternally or mounted on an external surface of the vehicle 100 and maybe used by computing device 110 to provide information to potentialpassengers or other persons outside of vehicle 100.

In one example, computing device 110 may be an autonomous drivingcomputing system incorporated into vehicle 100. The autonomous drivingcomputing system may capable of communicating with various components ofthe vehicle. For example, returning to FIG. 1, computing device 110 maybe in communication various systems of vehicle 100, such as decelerationsystem 160, acceleration system 162, steering system 164, signalingsystem 166, navigation system 168, positioning system 170, andperception system 172, such that one or more systems working togethermay control the movement, speed, direction, etc. of vehicle 100 inaccordance with the instructions 134 stored in memory 130. Althoughthese systems are shown as external to computing device 110, inactuality, these systems may also be incorporated into computing device110, again as an autonomous driving computing system for controllingvehicle 100.

As an example, computing device 110 may interact with decelerationsystem 160 and acceleration system 162 in order to control the speed ofthe vehicle. Similarly, steering system 164 may be used by computingdevice 110 in order to control the direction of vehicle 100. Forexample, if vehicle 100 configured for use on a road, such as a car ortruck, the steering system may include components to control the angleof wheels to turn the vehicle. Signaling system 166 may be used bycomputing device 110 in order to signal the vehicle's intent to otherdrivers or vehicles, for example, by lighting turn signals or brakelights when needed.

Navigation system 168 may be used by computing device 110 in order todetermine and follow a route to a location. In this regard, thenavigation system 168 and/or data 132 may store map information, e.g.,highly detailed maps identifying the shape and elevation of roadways,lane lines, intersections, crosswalks, speed limits, traffic signals,buildings, signs, real time traffic information, vegetation, or othersuch objects and information.

Positioning system 170 may be used by computing device 110 in order todetermine the vehicle's relative or absolute position on a map or on theearth. For example, the position system 170 may include a GPS receiverto determine the device's latitude, longitude and/or altitude position.Other location systems such as laser-based localization systems,inertial-aided GPS, or camera-based localization may also be used toidentify the location of the vehicle. The location of the vehicle mayinclude an absolute geographical location, such as latitude, longitude,and altitude as well as relative location information, such as locationrelative to other cars immediately around it which can often bedetermined with less noise that absolute geographical location.

The positioning system 170 may also include other devices incommunication with computing device 110, such as an accelerometer,gyroscope or another direction/speed detection device to determine thedirection and speed of the vehicle or changes thereto. By way of exampleonly, an acceleration device may determine its pitch, yaw or roll (orchanges thereto) relative to the direction of gravity or a planeperpendicular thereto. The device may also track increases or decreasesin speed and the direction of such changes. The device's provision oflocation and orientation data as set forth herein may be providedautomatically to the computing device 110, other computing devices andcombinations of the foregoing.

The perception system 172 also includes one or more components fordetecting and performing analysis on objects external to the vehiclesuch as other vehicles, obstacles in the roadway, traffic signals,signs, trees, etc. For example, the perception system 172 may includelasers, sonar, radar, one or more cameras, or any other detectiondevices which record data which may be processed by computing device110. In the case where the vehicle is a small passenger vehicle such asa car, the car may include a laser mounted on the roof or otherconvenient location.

The computing device 110 may control the direction and speed of thevehicle by controlling various components. By way of example, if thevehicle is operating completely autonomously, computing device 110 maynavigate the vehicle to a location using data from the detailed mapinformation and navigation system 168. Computing device 110 may use thepositioning system 170 to determine the vehicle's location andperception system 172 to detect and respond to objects when needed toreach the location safely. In order to do so, computing device 110 maycause the vehicle to accelerate (e.g., by increasing fuel or otherenergy provided to the engine by acceleration system 162), decelerate(e.g., by decreasing the fuel supplied to the engine or by applyingbrakes by deceleration system 160), change direction (e.g., by turningthe front or rear wheels of vehicle 100 by steering system 164), andsignal such changes (e.g. by lighting turn signals of signaling system166).

FIG. 1B is an example illustration of vehicle 100 described above. Asshown, various components of the perception system 172 may be positionedon the roof of vehicle 100 in order to better detect external objectswhile the vehicle is engaged. In this regard, one or more sensors, suchas laser range finder 182 may be positioned or mounted to the roof ofvehicle 101. Thus, the computing device 110 (not shown) may controllaser range finder 182, e.g., by rotating it 180 degrees, or one or morecameras 184 mounted internally on the windshield of vehicle 100 toreceive and analyze various images about the environment. Although thelaser range finder 182 is positioned on top of perception system 172 inFIG. 1B, and the one or more cameras 184 mounted internally on thewindshield, other detection devices, such as sonar, radar, GPS, etc.,may also be positioned in a similar manner.

As noted above, a height profile of a vehicle, e.g., vehicle 100, may bestored in memory 130 of computing device 110. FIG. 2 depicts an exampleheight profile 200 of vehicle 100. As shown, height profile 200 may bebased on a virtual model 202 of the vehicle 100. The virtual modelrepresents a general three-dimensional shape, dimension, and/or geometryof the vehicle 100. When determining whether vehicle 100 can maneuverunder or around a particular object, the perception system 172 may useand depend on the width and height measurements of the vehicle. Asshown, a height profile may be generated based on the back view of thevirtual model 202 by measuring lateral distances from a center line 210(perpendicular to the lateral distances) to either side of the vehicle100 at various height measurements ascending from bottom to top of thevehicle, or vice versa. Thus, the center line 210 may establish symmetrybetween the two sides of the vehicle 100.

As noted above, a set of lateral distances from the center of thevehicle may be measured at various height measurements. As shown in FIG.2, lateral distance 220 is measured from the center line 210 to the leftside of the virtual model 202 at a first height measurement. Similarly,lateral distance 222 is measured from the center line 510 to the leftside of the virtual model 202 at a second height measurement. Additionallateral distances may be measured in a similar manner at third, fourth,fifth, etc. height measurements up to the top of vehicle 100. In oneaspect, the height measurements may be intervaled, such that thevertical spacing between one lateral distance to another is equivalent.

A height profile may be represented by an array of width-heightmeasurements that may correspond to the lateral distances. For example,the height profile 200 of virtual model 202 may include an array of (x,y) values, where “x” represents the lateral distances from the centerline 210 in meters and “y” represents the height measurements in meters.As shown in chart 240, the rows associated with the first column 242 ofchart 240 correspond to the lateral distances of the virtual model 202from the center line 210 to the left side of vehicle 100. The rowsassociated with the second column 244 of chart 240 correspond tointervaled height measurements. The rows associated with the thirdcolumn 246 of chart 240 correspond to the array of (x, y) values of thefirst and second columns.

For instance, the first 10 lateral distances for vehicle 100 at heightmeasurements 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 meterscorrespond to 1.4 meters. At height measurements 2.2, 2.4, 2.6, 2.8 and3.0 meters, the associated lateral distances for vehicle 100 correspondto 0.6 meters, 0.5, 0.4, 0.3, and 0.4 meters, respectively. As theheight measurements are incremented, the lateral distances change invalue as they conform to the dimensions of the virtual model 502 ofvehicle 100.

While the height profile 200 depicted in FIG. 2 is measured from theleft side of the virtual model 202 of vehicle 100, the height profilemay also be measured from the right side of vehicle 100. Further, whilechart 240 includes 3 columns and 15 rows organizing the lateral distanceand height measurement values, the chart may be organized in other waysand include different types of measurements. In addition, the dataassociated with the height profile does not need to be represented as achart, but may be represented or organized in various ways.

In addition to the operations described above and illustrated in thefigures, various operations will now be described. It should beunderstood that the following operations do not have to be performed inthe precise order described below. Rather, various steps can be handledin a different order or simultaneously, and steps may also be added oromitted.

A vehicle may detect various objects on and/or near the vehicle'strajectory and perform clearance measurements, as detailed below. FIG. 3is an example illustration 300 of an autonomous vehicle detectingvarious objects along a particular trajectory. In this example,autonomous vehicle 100 may be traveling along road 312 in a geographicarea 310, such as a suburban neighborhood. As shown, the vehicle 100 istraveling eastbound along trajectory 314 on road 312.

As the vehicle 100 travels along its trajectory, the vehicle'sperception system 172 may detect and identify various objects near road312 to maneuver around them, if necessary. For instance, the perceptionsystem 172 may detect trees 320, 322, 324, 326, 328, and 330. Inaddition, the perception system 172 may also detect fire hydrant 340 aswell as other objects, such as parked vehicles (not shown) along road412, traffic signs, trash bins, recycling bins, pedestrians, etc.

A perception system 172 of an autonomous vehicle may determine abounding box for each detected object. A bounding box may be a virtual,three-dimensional box that may completely enclose detected 3D pointscorresponding to an object and also includes a set of measurements(e.g., length, width, height) unique to the bounding box associated withthe object. For instance, the perception system 172 of vehicle 100identifies objects, such as trees 320, 322, 324, 326, 328, 330 and firehydrant 340, and arranges them into bounding boxes using at least a setof obstacle points based on the laser data derived from the laserrangefinder 182. The set of obstacle points may be used to determine thebounding box. As an example, tree 320 may be larger than fire hydrant340, thus the dimensions of bounding box corresponding to tree 320 maybe comparatively greater than the dimensions of bounding boxcorresponding to fire hydrant 340.

In addition, perception system 172 of an autonomous vehicle may usethese bounding boxes to determine where certain objects are spatiallylocated relative to the location of the vehicle. By way of example only,referring to FIG. 3, the perception system 172 of vehicle 100 mayidentify that trees 320 and 322 are across the road 312 from each other.Further, the perception system 172 may identify that trees 324 and 326are adjacent to one another, with fire hydrant 340 across the road 312.Finally, the perception system 172 may identify that trees 328 and 330are adjacent to another. In this regard, the perception system 172 maycommunicate and relay information to the computing device 110 of vehicle100, so that computing device 110 may safely maneuver vehicle 100 withinthe geographic area 310.

In one aspect, perception system 172 may identify a set of nearbyobjects along the vehicle's trajectory. In this regard, the perceptionsystem may temporarily disregard objects that are far away. By way ofexample only, the perception system 172 of vehicle 100 may establish athreshold distance 350 from the vehicle 100 to determine which objectsto include in the set of nearby objects. As shown, a boundary of thethreshold distance 350 may be a radial distance from vehicle 100.Alternatively, the threshold distance may be defined as a rectangle orfollow the contour of the road, etc.

Using threshold distance 350, the perception system may determine thattrees 320 and 322 lie within the boundary of threshold distance 350, andthus include trees 320 and 322 in the set of nearby objects. And sincetrees 324, 326, 328, and 330 as well as fire hydrant 340 lie outside theboundary of threshold distance 350, they may be temporarily disregardedby the perception system for the purposes of analysis of clearancemeasurement.

In some instances, an object may not entirely occupy the space of thebounding box. By way of example only, a bounding box containing a treewith a long overhanging branch may not accurately represent the actualshape of the tree. For instance, if the long branch of aforementionedtree overhangs the vehicle's trajectory, the associated bounding box mayprotrude into the trajectory. Thus, the computing device of the vehiclemay generate a more accurate representation of the tree bythree-dimensionally projecting a set of corresponding obstacle points.Thereafter, a cross-section or “slice” of the bounding box closest tothe vehicle and perpendicular to the direction of the vehicle's movementmay be used to generate a two-dimensional contour of the object based ona subset of obstacle points. Based on this contour, the vehicle maydetermine whether it should maneuver under or around the tree.

FIG. 4A illustrates a bounding box 410 enclosing tree 320. As shown, thebounding box 410 generally exhibits the width, length, and heightdimensions corresponding to the dimensions of the tree 320. In addition,the bounding box corresponding to the tree 320 may include a largeamount of empty space at least below the tree's overhanging branch. Forexample, the perception system 172 of vehicle 100 may determine thatbounding box 410 protrudes out into road 312 since bounding box 410entirely encloses tree 320 (including the overhanging branch). In thatregard, the computing device 110 of vehicle 100 may determine that tree320 is impeding vehicle 100's trajectory 314 and determine how close thevehicle can maneuver relative to the tree 320.

In one example, a perception system may project a set of obstacle pointscorresponding to an object in order to determine a contour of theobject. FIG. 4B illustrates a set of obstacle points 420 correspondingto tree 320. For example, the perception system 172 of vehicle mayidentify the set of obstacle points 420 within bounding box 410. Asshown, the obstacle points 420 correspond to the shape of tree 320. Eachobstacle point may be associated with a coordinate within the boundingbox 610, such as (x, y, z), where x, y, and z represent the width (e.g.,x-axis), the length (e.g., y-axis), and the height (e.g., z-axis) ofbounding box 610, respectively. The coordinates may indicate the spatialposition of the obstacle points.

Using the set of obstacle points, the perception system may take across-section or a slice of the bounding box 410 perpendicular to thevehicle's direction of movement 430 and use a subset of correspondingobstacle points to generate a two-dimensional contour of the tree 320.By way of example, as the vehicle 100 travels along each intervaled stepof its trajectory under tree 320, the perception system 172 may identifya plane closest to the vehicle and perpendicular to the vehicle'sdirection of movement 430. The plane may be a cross-section of boundingbox 410 and may also have a particular thickness. Moreover, the planemay contain a subset of the set of obstacle points determined in FIG.4B.

The plane may also be configured into a grid that includes a pluralityof grid cells. Based on which of these grid cells are occupied using thespatial position information of the subset of obstacle points, atwo-dimensional contour may be generated. As shown in FIG. 4C, atwo-dimensional contour 440 of tree 320 is outlined by the shaded gridcells. The computing device 110 of vehicle 100 may then use this contourto determine a height profile for the tree 320. Each grid cell may havea particular dimension, such as 20 cm, or more or less. The size of thegird cells (or the resolution of the grid) may be associated with thecalculation speeds and measurement accuracy. For example, smaller gridcells may increase accuracy, but in some instances, may also decreasecalculation speed. In another example, larger grid cells may increasecalculation speeds, but may decrease accuracy.

Based on the two-dimensional contour, the one or more computing devicesmay compute a set of clearance measurements and determine a minimumclearance measurement. FIG. 5 illustrates an example computation 500 ofa minimum clearance measurement. In one example, the computing device110 of vehicle 100 may initially determine the height profile of thetree in order to compute a minimum clearance. Similar to the heightprofile of virtual model 202 of vehicle 100 depicted in FIG. 2, theheight profile of tree 320 may be based on a set of lateral distancesfrom the center line 210 of the virtual model 202 to an edge or firstnon-empty grid cell shown of the two-dimensional contour 440 (shown inFIG. 4C) at various height measurements. As shown, the vertical heightmeasurements may correspond to the height measurements associated withthe height profile 200 of virtual model 202 (as seen in chart 240 ofFIG. 2).

Once the computing device 110 determines the height profile of the tree,the computing device 110 may then compute a set of lateral clearancemeasurements by taking the difference between the height profile ofvirtual model 202 and the height profile of tree 320. The set of lateralclearance measurements may be based on the difference between thelateral distances of the tree 320 and the lateral distances of thevirtual model 202. For example, the lateral distance 220 of heightprofile 200 may be subtracted from the lateral distance between centerline 210 and an edge of the two-dimensional contour 440. As depicted,these differences are represented by the dashed arrows, e.g., differencevalue 510.

Once a set of lateral clearance measurements are computed, the computingdevice 110 may determine that the smallest of these values is theminimum clearance measurement for the vehicle 100 and the object. Forinstance, the computing device 110 may determine that difference value510 is the smallest difference value and identify it as the minimumclearance measurement for the vehicle 100 at that intervaled step.

A minimum clearance measurement may be compared to the above-describedpredetermined threshold clearance value to ensure that a vehicle doesnot get too close to an object. For example, if computing device 110determines that the minimum clearance measurement, based on thedifference value 510, is less than the predetermined threshold clearancevalue, then the computing device 110 may determine that vehicle 100 canor cannot pass through the bounding box 410 corresponding to tree 320without hitting the overhanging branch or any part of the tree. When thecomputing device 110 determines that the vehicle 100 cannot pass throughthe bounding box 410, the computing device may maneuver the vehiclearound the bounding box 410.

FIG. 6 is a flow diagram 600 in accordance with aspects of thedisclosure. By way of the example depicted in FIG. 1 only, at block 602,computing device 110 of vehicle 100 may identify an object along a road.As discussed above, the object may be represented by a bounding box. Atblock 604, the computing device 110 may project a set of obstacle pointswithin the bounding box corresponding to the identified object. The setof obstacle points may be projected using laser data from at least thelaser rangefinder 182 of vehicle 100. As noted above, the set ofobstacle points may be used to ultimately determine whether the vehicle100 can safely maneuver relative to the object.

At block 606, the computing device 110 identifies a two-dimensionalplane oriented perpendicular to a direction of the movement of thevehicle. At block 608, the computing device 110 may determine whichareas of the two-dimensional plane are occupied based on the set ofobstacle points to generate a contour of the identified object. Asdiscussed above, this contour may be based at least in part on a grid.The grid may have a plurality of grid cells and the contour may be basedon which of the grid cells are occupied by an obstacle point. Using thiscontour, the computing device 110 may determine a height profile of theidentified object, at block 610. Subsequently, at block 612, thecomputing device 110 may identify a height profile of the vehicle 100.

At block 614, the computing device 110 may determine a minimum clearancebased on a height profile of the identified object and the heightprofile of the vehicle. As described above, one example of computing theminimum clearance is by taking the differences of the lateral distancesof the two height profiles. The lowest clearance measurement from a setof clearance measurements may be the minimum clearance. This minimumclearance measurement may be compared to a predetermined thresholdclearance to determine whether the vehicle 100 can safely maneuverrelative to the identified object.

Unless otherwise stated, the foregoing alternative examples are notmutually exclusive, but may be implemented in various combinations toachieve unique advantages. As these and other variations andcombinations of the features discussed above can be utilized withoutdeparting from the subject matter defined by the claims, the foregoingdescription of the embodiments should be taken by way of illustrationrather than by way of limitation of the subject matter defined by theclaims. In addition, the provision of the examples described herein, aswell as clauses phrased as “such as,” “including” and the like, shouldnot be interpreted as limiting the subject matter of the claims to thespecific examples; rather, the examples are intended to illustrate onlyone of many possible embodiments. Further, the same reference numbers indifferent drawings can identify the same or similar elements.

The invention claimed is:
 1. A method comprising: identifying, by one ormore computing devices having one or more processors, an object, whereinthe object is represented by a bounding box having a three-dimensionalvolume and a set of three-dimensional points within the bounding boxcorresponding to the identified object; projecting, by the one or morecomputing devices, the set of three-dimensional points into thethree-dimensional volume of the bounding box; maneuvering, by the one ormore computing devices, a vehicle towards the object at a particularheading; determining, by the one or more computing devices, atwo-dimensional plane oriented perpendicular to the particular heading;determining, by the one or more computing devices, a cross-sectionalarea of the bounding box having a three-dimensional volume and a subsetof the projected three-dimensional points, the cross sectional areacorresponding to a grid on the two-dimensional plane; identifying, bythe one or more computing devices, occupied cells of the grid;determining, by the one or more computing devices, a two-dimensionalcontour of the object within the bounding box based on the occupiedcells of the grid; and maneuvering, by the one or more computingdevices, the vehicle alongside of the object based on at least thedetermined two-dimensional contour and a predetermined thresholdclearance value.
 2. The method of claim 1, wherein determining thecross-sectional area includes identifying a plane closest to a virtualmodel of the vehicle defining a cross-sectional area of the vehicle. 3.The method of claim 1, further comprising determining a set of minimumclearance distances between a virtual model of the vehicle of thevehicle defining a cross-sectional area of the vehicle and thetwo-dimensional contour, and wherein maneuvering the vehicle alongsideof the object is further based on the set of minimum clearancedistances.
 4. The method of claim 3, wherein determining the set ofminimum clearance distances includes determining a height profile of theobject as a set of lateral distances between a center line of thevirtual model of the vehicle and the two-dimensional contour.
 5. Themethod of claim 3, wherein determining the set of minimum clearancedistances includes determining a set of difference values between (1) aset of lateral distances from a center line of the virtual model of thevehicle to an edge of the virtual model of the vehicle and (2) a set oflateral distances between a center line of the virtual model of thevehicle and the two-dimensional contour.
 6. The method of claim 3,further comprising identifying a smallest minimum clearance distance ofthe set of minimum clearance distances, and wherein maneuvering thevehicle alongside of the object is further based on the smallest minimumclearance distance.
 7. The method of claim 6, further comprisingdetermining that the smallest minimum clearance distance meets thepredetermined threshold clearance value before using the smallestminimum clearance distance to maneuver the vehicle.
 8. The method ofclaim 7, further comprising, when the smallest minimum clearancedistance does not meet the predetermined threshold clearance value,maneuvering the vehicle alongside of the object includes maneuvering thevehicle around the bounding box.
 9. The method of claim 1, whereinmaneuvering the vehicle includes maneuvering the vehicle alongside ofthe object at least partially within a location corresponding to thethree-dimensional volume of the bounding box.
 10. A system comprisingone or more computing devices having one or more processors, the one ormore computing devices being configured to: identify an object, whereinthe object is represented by a bounding box having a three-dimensionalvolume and a set of three-dimensional points within the bounding boxcorresponding to the identified object; project the set ofthree-dimensional points into the three-dimensional volume of thebounding box; maneuver a vehicle towards the object at a particularheading; determine a two-dimensional plane oriented perpendicular to theparticular heading; determine a cross-sectional area of the bounding boxhaving a three-dimensional volume and a subset of the projectedthree-dimensional points, the cross sectional area corresponding to agrid on the two-dimensional plane; identify occupied cells of the grid;determine a two-dimensional contour of the object within the boundingbox based on the occupied cells of the grid; and maneuver the vehiclealongside of the object based on at least the determined two-dimensionalcontour and a predetermined threshold clearance value.
 11. The system ofclaim 10, wherein determining the cross-sectional area includesidentifying a plane closest to a virtual model of the vehicle defining across-sectional area of the vehicle.
 12. The system of claim 10, whereinthe one or more computing devices are further configured to determine aset of minimum clearance distances between a virtual model of thevehicle of the vehicle defining a cross-sectional area of the vehicleand the two-dimensional contour, and to maneuver the vehicle alongsideof the object further based on the set of minimum clearance distances.13. The system of claim 12, wherein determining the set of minimumclearance distances includes determining a height profile of the objectas a set of lateral distances between a center line of the virtual modelof the vehicle and the two-dimensional contour.
 14. The system of claim12, wherein determining the set of minimum clearance distances includesdetermining a set of difference values between (1) a set of lateraldistances from a center line of the virtual model of the vehicle to anedge of the virtual model of the vehicle and (2) a set of lateraldistances between a center line of the virtual model of the vehicle andthe two-dimensional contour.
 15. The system of claim 12, wherein the oneor more computing devices are further configured to identify a smallestminimum clearance distance of the set of minimum clearance distances,and to maneuver the vehicle alongside of the object further based on thesmallest minimum clearance distance.
 16. The system of claim 15, furthercomprising determining that the smallest minimum clearance distancemeets the predetermined threshold clearance value before using thesmallest minimum clearance distance to maneuver the vehicle.
 17. Thesystem of claim 16, wherein the one or more computing devices arefurther configured to, when the smallest minimum clearance distance doesnot meet the predetermined threshold clearance value, maneuver thevehicle alongside of the object includes maneuvering the vehicle aroundthe bounding box.
 18. The system of claim 10, wherein maneuvering thevehicle alongside of the object includes maneuvering the vehicle atleast partially within a location corresponding to the three-dimensionalvolume of the bounding box.
 19. The system of claim 10, furthercomprising the vehicle.
 20. A non-transitory computer readable medium onwhich instructions are stored, the instructions, when performed by oneor more processors, cause the one or more processors to perform amethod, the method comprising: identifying an object, wherein the objectis represented by a bounding box having a three-dimensional volume and aset of three-dimensional points within the bounding box corresponding tothe identified object; projecting the set of three-dimensional pointsinto the three-dimensional volume of the bounding box; maneuvering avehicle towards the object at a particular heading; determining atwo-dimensional plane oriented perpendicular to the particular heading;determining a cross-sectional area of the bounding box having athree-dimensional volume and a subset of the projected three-dimensionalpoints, the cross sectional area corresponding to a grid on thetwo-dimensional plane; identifying occupied cells of the grid;determining a two-dimensional contour of the object within the boundingbox based on the occupied cells of the grid; and maneuvering the vehiclealongside of the object based on at least the determined two-dimensionalcontour and a predetermined threshold clearance value.